A Reason to Go to Bed on Time

Our own experience tells us that getting too little sleep or traveling across multiple time zones can impair our ability to function. And people who work on the night shift or who habitually sleep too little are more likely to be obese or have diabetes. But what is it about these stresses that translate into faulty physiology? By simulating the life-style of a shift worker or world traveler in controlled laboratory conditions, Buxton et al. now find that prolonged, simultaneous disruption of our normal sleep and circadian rhythms affects the workings of our insulin-secreting pancreatic cells, creating a prediabetic state. And even worse, under these conditions, people show a drop in their resting metabolic rate that could translate into a yearly weight gain of more than 10 pounds.

Getting a firm handle on the effects of life-style changes such as sleep, activity schedule, and diet on pancreatic function is much easier in small animals than humans. But Buxton et al. successfully investigated these questions by hosting 21 human participants in a completely controlled environment for almost 6 weeks and simulating disturbances in sleep and circadian rhythms, while keeping diet constant and scheduling all activities. Because sleep and circadian rhythms are intimately related, they designed a special protocol to independently manipulate these variables. After a stabilization segment in which the participants had adequate sleep at the appropriate time within their circadian rhythms, the participants spent 3 weeks in which they got only 5.6 hours of sleep per 24-hour period, while simultaneously experiencing 28-hour circadian days—a state similar to 4 hours of jet lag accumulating each day. During this time, the participants were often trying to sleep at unusual times within their circadian cycle. A segment of 9 recovery days followed.

During the 3-week disruption, the participants’ glucose control went haywire, and they were unable to mount a sufficiently high insulin response after a meal, resulting in too much glucose in their blood, in some cases at a level considered prediabetic. This magnitude of disruption, coupled with a lower resting metabolic rate that also emerged during the 3 treatment weeks, could easily set the stage for development of diabetes and obesity, although the exact process by which this happens awaits further study.

These results carry a cautionary message for employers to guard against causing adverse metabolic effects in workers by their shift scheduling practices—and a reinforcement of your mother’s message to go to bed on time and get enough sleep.